Finished lubricants and greases used for various applications, including automobiles, diesel engines, natural gas engines, axles, transmissions, and industrial applications consist of two general components, a lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
Numerous governing organizations, including original equipment manufacturers (OEM's), the American Petroleum Institute (API), Association des Consructeurs d' Automobiles (ACEA), the American Society of Testing and Materials (ASTM), the Society of Automotive Engineers (SAE), and National Lubricating Grease Institute (NLGI) among others, define the specifications for lubricating base oils and finished lubricants. Increasingly, the specifications for finished lubricants are calling for products with excellent low temperature properties, high oxidation stability, and low volatility. Currently only a small fraction of the base oils manufactured today are able to meet the demanding specifications of premium lubricant products.
Syncrudes prepared from the Fischer-Tropsch process comprise a mixture of various solid, liquid, and gaseous hydrocarbons. Those Fischer-Tropsch products which boil within the range of lubricating base oil contain a high proportion of wax which makes them ideal candidates for processing into lubricating base oil stocks. Accordingly, the hydrocarbon products recovered from the Fischer-Tropsch process have been proposed as feedstocks for preparing high quality lubricating base oils. When the Fischer-Tropsch waxes are converted into Fischer-Tropsch base oils by various processes, such as hydroprocessing and distillation, the base oils produced usually fall into different narrow-cut viscosity ranges. Typically, the kinematic viscosity of the various cuts will range between 2.1 cSt and 12 cSt at 100 degrees C. Since the kinematic viscosity of lubricating base oils typically will fall within the range of from 3 to 32 cSt at 100 degrees C., the base oils that fall outside of this viscosity range have limited use and, consequently, have less market value for engine oils.
The Fischer-Tropsch process typically produces a syncrude mixture containing a wide range of products having varying molecular weights but with a relatively high proportion of the products characterized by a low molecular weight and viscosity. Used by itself, this low viscosity product is not suitable for many lubricant applications, especially high volume applications, such as for engine oil. Currently, those Fischer-Tropsch derived base oils having kinematic viscosities below 3 cSt at 100 degrees C. have a limited market and are usually cracked into lower molecular weight material, such as diesel and naphtha. However, diesel and naphtha have a lower market value than lubricating base oil. It would be desirable to be able to upgrade these low viscosity base oils into products suitable for use as a lubricating base oil.
Conventional base oils prepared from petroleum derived feedstocks having a kinematic viscosity below 3 cSt at 100 degrees C. have a low viscosity index (VI) and high volatility. Consequently, low viscosity conventional base oils are unsuitable for blending with higher viscosity conventional base oils because the blend will fail to meet the VI and volatility specifications for many finished lubricants. Surprisingly, it has been found that Fischer-Tropsch derived base oils having a kinematic viscosity above 2 and below 3 cSt at 100 degrees C. display unusually high VI's, resulting in excellent low temperature properties and volatilities similar to those seen in conventional Group I and Group II light neutral base oils which have a kinematic viscosity generally falling in the range of between 3.8 and 4.7 cSt at 100 degrees C. Even more surprising was that when the low viscosity Fischer-Tropsch derived base oils were blended with certain Fischer-Tropsch derived bottom fractions or bright stock, a VI premium was observed, i.e., the VI of the blend was significantly higher than would have been expected from a mere averaging of the VI's for the two fractions. Consequently, it is has been discovered that the low viscosity Fischer-Tropsch base oils fractions may be advantageously employed as blending stock to prepare premium lubricants.
While Fischer-Tropsch derived lubricating base oil blends have been described in the prior art, the method used to prepare them and the properties of the prior art blends differ from the present invention. See, for example, U.S. Pat. Nos. 6,332,974; 6,096,940; 4,812,246; and 4,906,350. It has not been previously taught that Fischer-Tropsch fractions having a viscosity of less than 3 cSt at 100 degrees C. could be used to prepare lubricating base oils suitable for blending finished lubricants meeting the specifications for SAE Grade 10W, and 15W multigrade engine oils; monograde engine oils, automatic transmission fluids; and ISO Viscosity Grade 22, 32, and 46 industrial oils. With the present invention, this becomes possible.
When referring to conventional lubricating base oils this disclosure is referring to conventional petroleum derived lubricating base oils produced using petroleum refining processes well documented in the literature and known to those skilled in the art.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” are intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.